Mining and blasting operations involve hazardous materials and thus safety is of utmost importance in all activities relating to such operations. One of the primary activities of a blasting operation is borehole loading in which an explosive is loaded into a previously drilled borehole, and detonated. The explosive is commonly an emulsion explosive containing ammonium nitrate (which may be referred to as Ammonium Nitrate Emulsion or ANE). The ANE is typically pumped into a borehole using a pump attached to a hose. However, due to its highly viscous nature, ANE can be difficult to pump, particularly over long distances (for example, when loading deep boreholes) and/or through small diameter hoses used in borehole loading. Furthermore, there are often many boreholes to be loaded on a blasting bench or stope and the process can be quite time consuming Just-in-time manufacture of the ANE (immediately before borehole loading may also result in the use of ANE at elevated temperatures and greater time spent loading boreholes can further reduce the pumpability of high temperature ANE elevating the safety hazards—most notably pump pressure.
In most industries, elevated pump pressure associated with transportation of high viscosity fluids through pipes is averted by using large diameters pipes of minimal length. However, several factors prevent the use of large diameter, short length pipes in loading of ANE into boreholes. These include, for example: the need for transportation of a borehole-loading-delivery system (such a mobile manufacture unit or MMU) around a mine site from borehole to borehole; borehole characteristics—including depth, diameter and direction; and difficulty in accessing boreholes, especially in underground mining. Instead, long, flexible and often narrow loading hoses must be used to transfer ANE from the delivery system into a borehole. The length of an ANE loading hose is typically 30 to 60 meters but can be longer, depending upon the depth of the borehole.
The diameter of the borehole being loaded may also be a factor in determining the size of the hose. The inner diameter of hose that can be used may be as narrow as 19 mm. Transfer of ANE through such a narrow diameter hose at suitably high volumetric flow rate can require pumping pressures in excess of safe levels.
Several methods have been used to ensure that pumping pressures are maintained within an acceptable range. For example, it is known to use an annular stream of aqueous solution around a core stream of ANE being pumped through the hose. The aqueous solution serves to lubricate ANE delivery through the hose. This approach is known as “core annular flow” and the aqueous solution often referred to as a “water-ring” with the ANE being referred to as a “core”. However, under certain conditions the lubricating annular stream can be displaced or destroyed resulting in hose blockage and/or stalling of the delivery pump. In the industry this is known as “fouling”, and it causes considerable disruption to operations as well as being a safety hazard.
These problems commonly occur when the ANE is conveyed at elevated temperature, for example when ANE is manufactured in a just-in-time manner, without time for cooling prior to delivery through the hose. Elevated ambient temperatures may reduce the ability the cool the ANE. In this case water in the annular stream may migrate into the ANE by osmosis due to concentration effects, thereby degrading the annular stream. Higher emulsion temperatures also reduce ANE viscosity, which may cause inconsistent flow of the core.
The lubricating annular stream may also be impaired or destroyed when ANE remains in the hose, for example when the MMU moves from borehole to borehole and/or when the ANE is conveyed over long distances, such as when loading deep boreholes. Regular flushing of the hose is therefore required to un-block or reduce fouling of the hose.
Ground conditions on a mine site, such as the quality of borehole preparation, ease of borehole access, level of ruggedness of terrain, etc., can further slow borehole loading. ANE remains in the hose while dealing with these challenges which further increases the risk of hose fouling.
Displacement or destruction of the lubricating aqueous solution provided as the annular stream can also occur due to density differences between the aqueous solution and the ANE. The aqueous solution may contain chemical species (such as sodium nitrite) that are included to react with ammonium nitrate in the ANE in order to generate gas bubbles in the ANE that render it sensitive to detonation. Static head or pressure differential can be caused by the gas-generating reaction (commonly referred to as “gassing reaction”) commencing in the hose, or a combination thereof. At times, water present in the gassing solution can be absorbed by osmosis to the higher salinity of the ANE resulting in concentration of chemical species in the aqueous annulus and ultimately destruction of the annular stream. Destruction of the lubricating aqueous annular stream can also occur due to instability of the core annular flow. The stability of core annular flow may be influenced by the volumetric ratio and relative viscosity of the core and annular component. Core annular flow instability may also result in hose fouling.
Efforts to address displacement and destruction of the lubricating aqueous solution provided as the annular stream have included, for example:                Reducing ANE temperature, either through active cooling e.g. a heat exchanger or passive cooling e.g. increased inventory. However, both of these options are capital intensive due to the low thermal conductivity of ANE.        Managing the loading process in order to minimise down-time between holes.        Adjusting pH or the gassing reaction catalyst level to control or slow down the rate of the gassing reaction.        Adjusting the density of the aqueous solution to closer match that of the ANE to prevent segregation of the aqueous solution and ANE during down-time.        Flushing the hose with water to remove ANE fouling the hose.        
Against this background it would be desirable to provide another way of improving delivery of an emulsion explosive, such as ANE, through a hose.